As a mathematical tool, quantum Cramér-Rao bound is not the only one for quantum
multiparameter estimation. Bayesian approach , , , , , including Ziv-Zakai family , , 
and Weiss-Weinstein family , , and some other
tools , ,  like Holevo bound [1]}, , ,
have also shown their validity in various multiparameter scenarios. These tools
beyond the Cramér-Rao bound will be thoroughly reviewed by M. Guţă
et al.  in the same special issue and hence we do not discuss them
in this paper. Please see reference  for further reading of this
topic. In some scenarios in quantum parameter estimations, there may exist some
parameters that not of interest but affect the precision of estimating other
parameters of interest, which is usually referred to as the nuisance parameters.
Suzuki et al.  has thoroughly reviewed the quantum state estimation
with nuisance parameters in the same special issue. Please see reference 
for further reading.
